(1) Field of the Invention
The present invention relates to power supplies and more particularly to a bi-lateral four quadrant power converter.
(2) Description of the Prior Art
Four quadrant power converters are required for telephone ringing supply generators. Typically a high voltage (100 VRMS), low frequency AC signal is superimposed on a -50 VDC source. Four quadrant operation is required because, during ringing, only AC current flows into the load which may be highly reactive, causing the current to lead or lag the supplied AC voltage.
Most power converters supply a DC regulated output voltage in a single quadrant. An example of such a converter is a positive supply which delivers a positive current but cannot sink a negative current if power happens to be momentarily supplied by the load. Class AB DC coupled amplifiers, such as those used in high fidelity applications, can obtain isolation from the power source and provide four quadrant operation. However, to do this, two separate power supplies are used to supply current to a class AB linear or class D switching output stage. However, none of these amplifiers is bi-lateral and are therefore incapable of passing power in two directions.
Four quadrant operation is obtained in telephone ringing generators through use of the fixed office battery connected in series with a low frequency generator and having a large output coupling transformer. In such a generator both the battery and the transformer coupled generator, if driven appropriately, can carry current in both directions. However such an arrangement is inefficient and unsuitable for modern power requirements.
A recent advancement in the state of the art of power converters is the two quadrant converter disclosed by Slobodan Cuk at the IEEE Power Electronics Specialist Conference, 1977 record, pages 160-179. Two of these converters, one positive and one negative, could be connected in series to provide four quadrant operation. However, two supplies including two power pulse transformers are necessary to provide both output polarities.
Accordingly it is the object of the present invention to provide a bi-lateral, four quadrant power converter capable of not only applying power to the load but also passing power from output to input if the load voltage exceeds the intended supply voltage.